Sound reproducing unit and method for making the same



March 20, 1945 G. E. GUSTAFSON SOUND HEPRODUCI NG UNIT AND METHOD FORMAKING THE SAME Filed April 23, 1943 Metal mmvrox.

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0 5W A m w rwB m I Patented M. 20, 1945 scum) amonucmd UNIT AND METHOD 1non MAKING 'rna sum Gilbert E. Gustafson, River Forest, 211., minortoknith Radio corporation, a corporation of Illinois Application'April 2a,1943, Serial No. 484,153

, 1's Claims. (c1. 179-107) This invention relates to sound reproducingdevices and a method for making the same.

In many sound reproducing systems, and especially in hearing aid appratus, it is essential that the sound reproducing unit be orsmall size,inexpensive and 01' sturdy construction. Here tofore these desideratawere not always attained,

Figure 5 is a sectional view taken substantially ion line !--5 of baseII in Figure 6 in the absence because much skill and time were requiredto provid the correct air gap distance between ac.- tuating magnets andthe associated movable diaphragm, because the parts of the system wereof small'dimensions, and because there was a large number of partsmaking up the composite sound reproducing unit.

It is therefore an object of this invention to provide a small, compact,inexpensive and sturdy sound reproducing unit especially suitable foruse in hearing aids.

Another object of this invention is to provide a new and improved soundreproducing unit in which there is provided an air gap between actuatingmagnets and associated diaphragm of ac curate dimension, which gap ismaintained fixed with a high degree of stability.

Another object of this invention is to provide a small, compact, sturdysound reproducing unit having 9, minimum number or parts.

Another object of this invention is to provide a new and improved methodfor assembling the parts of a sound reproducing unit which lends itselfto mass production and yet insures a constant and stable air gapdistance between actuating magnets and diaphragm.

This is the parent of a divisional application, filed March 11, 1944,Serial No. 526,094, in which claims are directed particularly to theprocess ofmaking sound reproducing units described herein.

The features of my invention which I believe to be novel are set forthwith particularity in the a pended claims. My invention itself, both asto its organization and manner of operation, together with furtherobjects and advantages thereof, may best be understood by reference tothe following description taken in connection with the accompanyingdrawing in which:

Figure 1 is an exploded view of one embodiin practicing the method of myinvention to pro duce a unit as illustrated in Figure 1;

of pole pieces HA, HA and yoke II. v

Figur 6 is a perspective view showing apparatus for moulding the base ofthe unit shown in Figure 1, the section through the base being of apartially assembled unit as produced by the cementing process in Fig.'l;

Figure I is a view partly in elevation and partly in section showing theassembled jig of Figure 4 mounted with the cooperating base member Inillustrated in Figure 1 arranged to practice the method of my invention;the sectional part being taken on a line corresponding to lines 1-!ofboth Figs. 4 and 6.

Referring toFigure 1, the sound reproducing, unit comprisesa base It],pole pieces II and i2, permanent magnet yoke i2, magnet coils l4 and ll,terminals l6. and I1, diaphragm l8 and cover l9. v The base I0 is ofinsulating material, suchfas Bakelite or the like, and has an innercir'cular ledge 20 upon which the diaphragm l8 normally rests. The baseto has also a second lower inner ledge 2| upon which the terminals IEand H are fastened (preferably by means of screws ISA and "A or thelike), and still lower oppositely disposed ledges 22 and 23 (see Fig. 6)uponwhich the magnet coils, It and I! rest. The base In has also acentrally located recess 24 in which the pole pieces H and I2 and yokei3 are snugly received and in which theyare fastened by means to bedescribed later. The base "I hastwo parallelly extending and integrallyformed portions 25 and 26 in each of which is a hole adapted to receivea rod shaped electrical contact member (not shown), so that suchelectrical contact members, when inserted in the portions 25 and 26,make electrical connection with the terminal portions 21 and 28 ofterminals I6 and H, which portions 21 and 28 extend through base holes29 and 30 (see Fig. 6) into the portions 25 and 26 V v of the base Ill.

The base ill, of Bakelite or other similar material capable o1 beingmolded in suitable form and shape to form the various ledges and re-vcesses and integrally formed projecting portions, is formed between apair of cooperating dies and il. in Fig. 5, the inner surface 620i dieQB being of the same shape as the outside surface 0 base member I B andthe outerfsliifi'ace 63 of GI having the same contour as the i"ofbasememberlfl.

In the manufacture of base'memb or similar material is placed in die 0,the die I is then placed in cooperating relationship with die 80 withthe Bakelite or similar moldable material therebetween, and the Bakeliteis caused to solidify by applying heat thereto in well-known manner,with the result that when the dies II and 6| are separated from eachother and 1mm the solid Bakelite, "base member Iii is produced. Terminalholes are then drilled by conventional means in base ortions 25' and 26for a purpose described later. r

The yoke I3 is of magnetic material, preferably Alnico, an alloy 01'iron, aluminum, nickel and cobaltdn such proportions that the alloy hasgreat permanence and coercive force. It

abuts against and holds the pole pieces H and I2 1 in spacedrelationship.

The magnet coils it and I are wound on bob- .bins HA and ISA which haverectangularly shaped hollow cores MB and I53 which maybe pressed overthe smaller portions HA and [2A 01' pole pieces H and I2 which extendtherethrough.

The diaphragm l8 comprises a thin disk having concentrically mountedthereon a smaller disk IBA sufllcient to increase the central thicknessof the diaphragm l8 so that it can carry the magnetic flux from yoke l3and coils II and I 5 without undesirable saturation.

The cover l9 has a circular shoulder ISA (see Fig. 8) adapted to engagetightly against the inner wall of base In but not or suiiicient verticalextent to bottom against diaphragm l8. It also has an extending tubularprojection 19B adapted to receive a. sound transmitting-.element.*- Inop-:

eration, the cover I! is substantially stationary and the sound impulsesgenerated by movement oi diaphragm I 8 are transmitted through coveropening I90.

The pole pieces II and I2 and yoke II are cemented in and to the baseIII by a suitable material such as an alloy as shown in Fig. 3. One

heated, preferably by induction heating (see coil 42 in Fig. '7), and,when the alloy cools, the yoke l3 and pole pieces H and I2 are'heldfirmly in place in and on the insulating base Hi. The bobbins HA and HAsupporting coils II and I! are then pressed onto pole tips' HA and "A,and terminals l6 and I! are then fastened on ledge 2|, preferably byscrews or rivets. with the terminal projecting portions 21 and 28extending into the base portions and 28, whereby electrical contact maybe made with them when rod shaped electrical conducting members (notshown)- are inserted into the holes in base portions 25 and 28. Thediaphragm I8 is then placed on bas ledge 20 and is held thereon due tothe action of the magnetized pole pieces H and I2. The cover I8 is thenlaced on the base and is frictionally The parts cemented preferably haveprepared surfaces thereon so as to increase the area of the cementedsurface and so as to provide a finished structure, having increasedstrength. That is for this purpose. the pole pieces II and I2 areprovided with notches B and HE respectively,

the yoke II is provided with surfaces ISA hav-' ing indentations IIBtherein, and the base III is provided with indentations IDA thereinwhich may partake of a grooved surface.

In order to make the sound reproducing unit heretofore described in.mass production and with a predetermined constant distance between polepieces II and I2 and diaphragm i8, the jig shown in Figure 4 isutilized. It is important to realize that in small hearing aidreproducing units the pole pieces II and II are mounted approximately.01 inch below base ledge 20 upon which diaphragm l8 rides; and, thediaphragm and outer pole piece surface must be substantially parallelwith their separation tolerance in the order of a few percent.

The jig of Figure 4 comprises a circular base plate ll of such outerdiameter as to be trictionally held by the upper inner curved wall ofthe .basei ll. Shoulder 32 on base plate 3| serves to limit'the movementof base plate 3| into base II. In the exploded view, Figure 4, therectangular shaped collar 38 is adapted to contain snugly within itshollow portion the wedge 34, the pair of channel shaped wedge members 35and I, and parts HA and I2A of the pair of pole pieces H and I2.

In order to assemble the parts on the Jig, the

channel shaped wedge members Iii and 36 and parts" HA and HA of polepieces ii and I! are mounted on the base plate 3| within the rectangularring 23. with channel shaped wedge memhers I! and 38 in abuttingrelationship to the 40 downwardly extending portions HA and I2A of asuitable lowmelting point alloy includes bismuth pole pieces II and I2.-Then the screw 40 (Fig. '7),

having wedge shaped head 3|, i drawn against the cooperating channelshaped wedge members 35 and 38 by turning the nut Al. As nut H istightened on screw Ill wedge shaped head 34 is ing as in Figure 2.

drawn into engagement with cooperating wedge surfaces on channel members35 and 38, and the resulting outward movement "of channel members 35 andIt causes parts IA and HA of pole pieces H and I2 to be firmly held inthe encircling rectangular'shaped ring 33. Magnetic yoke I3 is thenplaced on ring 33 betwen the downwardly extending portions HA and Hit ofpole pieces H and i2 its magnetism holding it securely between polepieces II and I2. v

The assembled jig is of such dimensions that I when it is inserted inthe base Ill, containing the elements of the sound reproducing unit(such assembly being shown in Fig. '7), the shoulder 32 abuts the upperledg 20 of base ll (Fig. 6) with the pole pieces II and I2 and yoke l3inserted in base recess 2| in predetermined spaced relationship to thebase ledge 20 after the alloy material disposed between the base I0 andyoke I3 and pole pieces II and I2 melts.

It is noted that the alloy material initially placed in base In prior toinserting the jig therein is usually in powdered form thus causingshoulder 32 to be separated a small distance from the upper ledge 20 ofbase l0 when such jig is inserted into the base. But, when and as suchpowdered alloy melts, shoulder 32 approaches its position on the upperledge 2|! of base l0 either due to gravity forces acting on thecomposite jig due to other torces applied between base Ill and the lie.Ultimately shoulder" rests on the upper ledge 20 of base II and is heldin that position when and asthe alloy later solidifies due to gravityiorces, acting on the-composite jig or due to an external force appliedbetween i the Jig and base member ll.

When high frequency current is applied to the coil .42. (Fig. 7) the lowmelting point alloy material (or another suitable material), which wasinitially placed in base member ll around pole pieces II and I2 and yokeit. melts. Then, as the alloy material cools and solidifies after coil42 is deenergized, the alloy material expands slightly while shoulder 32is firmly held on the upper ledge 2| of base member l and when the alloymaterial solidifies entirely, it firmly holds the pole pieces II and I2and yoke I! to the base II with the races of pole pieces H and II in apredetermined spaced relationship with respect to the -'base ledge 20upon which the diaphragm I8 is subsequently placed. It is also notedthat when the expansible metal .alloy is heated by high frequencycurrents fiowing in coil 42, eddy currents flowing in such expansiblemetal produce a magnetic shielding eii'ect on pole pieces I I and I2 andmagnetic yoke l3 whereby less heat is generated in pole pieces II studl2 and yoke ll due to high frequency currents in coil 42 than thatproduced when the expansible metal is absent. This fe ire is ofparticul'ar importance since the magnetic state of pole pieces H and I2and yoke I3 is disturbed much less when eddy currents flow in theexpansible metal than is the case when such-expansible metal is absent.After the pole pieces H and I land yoke I 3 are thus cemented to thebase l0, they are disengaged from the jig by loosening nut 4| on screwll.

In the, preferred embodiment of this invention, the P01 pieces arecemented to the insulating frequency induction heating apparatus. It isalso apparent that the alloy material may be heated by means other thanby the preferred use of electrical induction heating apparatus and baseIll by alloy material which is heated by highasvae a of the pole piecesII and I2 with respect to base ledge 2|. It is noted that since the baserecess 24' snugly receives the pole pieces II and I2 and Yoke II. asmall clearance exists between the walls defining recess 24 throughwhich the material may pass with appreciable resistance'as it solidifiesand consequently a relativelylarge force is. exerted by the expandingmaterial between base l. and pole pieces II and I2. This expanding forceis utilized in accordance with the present invention to avoid voids andto establish an accurate air gap distance.

in the insulating base.

In the assembled jig the parts HA and I2A of pole pieces "and I2 abutthe base plate 3i and are of predetermined height, so as to assure theircorrect spacing in the fabricated sound reproducing device, the heightof shoulder 32 on base plate ll of the jig beingjust right to assuresuch correct spacing. V I

The cementing process described herein is accomplished by making use ofthe adhesive or binding properties of materials which set in cem'entingrelation between the parts toi be cemented whereby those parts can beplaced in predetermined space relationship, as in a jig, and held insuch relation when the cement sets. The cementing process is preferablycarried out by using a low melting point material having the property ofexpanding as it cools, and in which the material adheres to theFurthermore, it is noted that since pressure is applied to theexpansible alloy when and as it solidifies it is reasonable to believethat such alloy is in a somewhat stressed condition after the completesolidification process.

While I have shown and described particular embodlments'oi my invention.it will beobvious to those skilled in the art that changes andmodifications may be made without departing from my invention in itsbroader aspects, and I, therethis invention is not necessarily limitedto they preferred heating apparatus.

The fact that the preferred alloy material has a low melting point,-ismetallic and expands as it solidifies makes it a desirable cementingagent in this application. The fact that the material is metallic innature allows the use of induction heating apparatus and the surroundingparts necessary to place a sufllcient quantity of such alloy materialbetween the base ill and pole pieces I I and I2 in the assemblingoperations, such sufiicient quantity being of a thickness greater thanthe thickness present in the finished product, heating such materialabove its melting point and constraining the flow of such material to adegree as it solidifies such that the pole pieces II and I 2 are firmlypressed and tend to move outwardly against the force of gravity or otherexternal forces which act to maintain shoulder 32 in abuttingrelationship to the upper edge of 1 base l0, thus assuring predeterminedspacing tore, aim in the appended claims to cover all such changes andmodifications as fall within the true spirit andscope of my invention.

I claim l 1. In a sound reproducingunit, a base member of insulatingmaterial, and a pole piece fixedly mounted on said base in predeterminedspaced relationship thereto by metallic cement having the property ofexpanding as it solidifies.

2'. In a sound reproducing unit, a base member of insulating materialhaving a ledge, and a pole piece fixedly mounted by cement on said basein predetermined spacedgelationship to said ledge. said cement beinga-metal having the property of expanding as it solidifies.

3. In a' sound reproducing unit, a base memher having a recess and aledge, a pair of pole pieces, a magnetic yoke abutting against said polepieces and holding said pole pieces in spaced relationship, said polepieces and yoke being disposed in said recess and fixedly mounted bycementon the base member with the faces of said .pole pieces lying inpredetermined spaced relationship to the ledge, said cement being ofmetal having th property of expanding as it solidifies.

4; In a sound reproducing unit, a base member of insulating materialhaving a circular ledge and a recessed portion, a pair of pole pieces. amagnetieyoke' abutting against said pole pieces, said recess beingarranged to snugly receive said pole pieces and yoke, a magnetic coilfor each One 'of said pole pieces. said base member having a pair ofoppositely disposed ledges each supporting one of the magnet'coils, athin layer of metal parts being cemented I v metal cement having lowportions, a

net coils, said base member having a pair of opcement having theproperty ofcxpa'nding as it solidifies in said recess between said polepieces,

yoke andbase member, said layer of metal ce-- pair of oppositely d po edled es and each supporting one of the magnet coils, a thin layer of theproperty of expanding as it solidifies in said recess and disposedbetween said pole pieces, yoke and magnet coils and providing the solemeans for fastening the pole pieces in predetermined spaced relationshipto the first mentioned ledge, said metal cement being of predeterminedthickness for accurately spacing said pole pieces insaid base, said basemember having a pair of parallel extending holterminal for each one ofthe magpositely disposed ledges each adapted to support one of theterminal members, said base member having a channel extending from eachof the last mentioned ledges to each one of'the hollow por-.

tions, and said terminals each having a projection extending througheach channel and into the corresponding base hollow portion.

.6. In a sound reproducing unit, a base member having a recess, a pairof pole pieces, a magnetic yoke abutting said pole pieces and holdingsaid pole pieces in spaced relationship, said pole pieces and yokedisposed in said recess and fixedly mounted by cement on the base memberin preagainst said polepieces, ranged to' snugly receive said 10. In asound reproducing unit. a base member of insulating material, a polepiece in said base in predetermined spaced relationship therein, a thinlayer of metal cement having the property of expanding as it solidifiesand in a stressed condition disposed between the (pole piece and baseand providing the sole means for fastening the pole piece to the-base,said metal cementbeing of predetermined thickness for accurately spacingsaid pole piece in said base, said thin layer of metal cement beingheatable by induction.-heating to its melting point, I

11. Ina sound reproducing unit, a base member of insulating materialhaving a ledge, a pole piece in predetermined spaced relationship tosaid ledge, a thin layer of metal cement having the property ofexpanding as it solidifies disposed.

between the pole piece and base and providing the sole means forfastening the pole piece to the base in predetermined spacedrelationship to said ledge, said metal cement being heatable to l 7 itsmelting point by induction heating and said metal cement being sodisposed that eddy currents flowing therein when inductively heatedreduce the heating of said p'ole piece, said cement being ofpredetermined thickness for accurately spacing said pole piece withrespect to said ledge.

determined spaced relationship in said base, said cement being ametaLhaving the property of ex panding as it solidifies.

7. In a sound reproducing unit, a base mem-.

her having a recess, a pair of pole pieces, a magnetic yoke abuttingagainst said pole pieces and holding said pole pieces in spacedrelationship,

said pole pieces and yoke being fixedly mounted by cement in saidrecess, .and said pole pieces, yoke and base member having cooperatingsurfaces thereon adapted 'to readily hold said ce ment, said cementbeing a metal having the property of expanding as it solidifies.

8. In a sound reproducing unit, a base member of insulating material, apole piece in said base in predetermined spaced relationship therein, athin layer of metal cement having the property of expanding as itsolidifies and in a stressed condition disposed between the pole pieceand base and providing the sole means for fastening the pole piece tothe base, said metal cement be ing of predetermined thickness foraccurately spacing said pole piece in said base.

9. In a sound reproducing unit, a base member of insulating materialhaving a, ledge, a pole piece in predetermined spaced relationship tosaid ledge, a thin layer of metal cement having the property ofexpanding as it solidifies disposed.

between the pole piece and base and providing the sole means forfastening the pole piece to the base in predetermined spacedrelationship to said ledge, said metal cement being heatable to itsmelting point by induction heating and 12. In a sound reproducing unit,a base member of insulating material, a pole piece in'said base inpredetermined spaced relationship there' in, a thin layer of metalcement having. the property ofexpanding as it solidifies and in astressed condition disposed between the pole piece and base andproviding the sole means for fastening the pole piece to the base, saidmetal cement be-' ing of predetermined thickness for accurately spacingsaid pole piece in said base; said thin layer of metal cement beingheatable by induction heating to its melting point, said metalcement-being so disposed that eddy currents flow-' ing in said cementwhen heated produce a substantial magnetic shielding effect on .said'pole piece whereby the heating of said pole piece is reducedsubstantially when said'metal cement is inductively heated.

13. In a sound'reproducing unit, a base'mem- I per, a pole piece, andmetallic cementing material therebetween having the property ofexpanding asit solidifies to assure a correct spacing of said pole piecewith respect to a point on said base. ,1

14. In combination, in a'sound reproducing vunit, a base member, a polepiece, means for producing variable flux in said pole piece, a diaphragmactuated in response to said flux variations and .carried by said basemember, and means including metallic cementing material having theproperty of expanding as it solidifies interposed between said polepiece and diaphragm carrying member to assure a correct spacing of saidpole piece with respect to a point on said being of predeterminedthickness for accurately spacing said pole piece with respect to saidledge.

15. A sound reproducing unit comprising resillent means composed atleast in part of magnetic material for actuating the air to producesound waves, electromagnetic means responsive to elec trlc currents ofvoice frequency for producing a magnetic field to drive said resilientmeans, a

base member supporting said resilient means and unit adiacent theretobeing shaped so as to be locked together against relative movement whensaid alloy is in a solid condition, thereby to maintain saidpredetermined space relationship.

16. A sound reproducing unit comprising resilient means composed atleast in part of magnetic material for actuating the air to producesound waves, electromagnetic means responsive to electric currents ofvoice frequency for producing a magnetic field to drive said resilientmeans, a base member of insulating material supporting said resilientand electromagnetic means,

electromagnetically shielded thereby from heating when said spacer isinductively-heated.

GILBERT E. GUSTAFSON.

CERTIFICATE OF CORRECTION;

Patent No 2 571 819.

It is hereby certified that error appears in the. printed specificationof the above numbered patent requiring correction as follows: Page 1,second column, lines 14. to 6 inclus ive", strike out "showing apparatusfor moulding the'ba se of the unit shown in Figure 1, the sectionthrough the base being" and insert the same after "view" in line 1, samepageand column, and

.that the said Letters Patent should be read with this correctiontherein that the same-may conform to the record of the case in thePatent Office.

March 20, 1914.5.-

GILBERT E GUSTAFSON.

Signed and sealed this 19th day or June, A. 12.1915.

(Seal) Leslie Frazer Acting Commissionerof Patents.

locked together against relative movement when said alloy is in a solidcondition, thereby to maintain said predetermined space relationship.

16. A sound reproducing unit comprising resilient means composed atleast in part of magnetic material for actuating the air to producesound waves, electromagnetic means responsive to electric currents ofvoice frequency for producing a magnetic field to drive said resilientmeans, a base member of insulating material supporting said resilientand electromagnetic means,

electromagnetically shielded thereby from heating when said spacer isinductively-heated.

GILBERT E. GUSTAFSON.

CERTIFICATE OF CORRECTION;

Patent No 2 571 819.

It is hereby certified that error appears in the. printed specificationof the above numbered patent requiring correction as follows: Page 1,second column, lines 14. to 6 inclus ive", strike out "showing apparatusfor moulding the'ba se of the unit shown in Figure 1, the sectionthrough the base being" and insert the same after "view" in line 1, samepageand column, and

.that the said Letters Patent should be read with this correctiontherein that the same-may conform to the record of the case in thePatent Office.

March 20, 1914.5.-

GILBERT E GUSTAFSON.

Signed and sealed this 19th day or June, A. 12.1915.

(Seal) Leslie Frazer Acting Commissionerof Patents.

